This invention relates to the sorting of metal scrap constituted of a mixture of scrap metal pieces of two or more different alloy compositions, so as to separate the metal pieces of one composition from the other or others. More particularly, it is directed to methods of marking aluminum sheet for scrap sorting purposes.
As used herein, the term xe2x80x9caluminumxe2x80x9d refers to aluminum metal and aluminum-based alloys, viz., alloys containing more than 50% by weight aluminum. xe2x80x9cScrapxe2x80x9d refers to pieces of metal in solid as distinguished from molten state.
An important and illustrative field of use for such methods (to which, however, the invention in its broader aspects is not limited) is the sorting of manufacturing scrap generated incident to automobile manufacturing operations utilizing aluminum sheet. The production of automobile body components or other automotive parts by forming aluminum sheet generates substantial quantities of metal scrap, i.e., pieces of metal from the sheet stock subjected to the forming and related operations such as trimming. The term xe2x80x9cmanufacturing scrapxe2x80x9d is used herein to differentiate such scrap from post-consumer scrap (generated from used and discarded manufactured articles). Manufacturing scrap differs from post-consumer scrap in that, being generated incident to forming operations, manufacturing scrap does not bear a paint or other permanent opaque coating on its major surfaces, whereas post-consumer scrap often has major surfaces more or less covered with paint or other substances applied after forming.
As is well known, for both environmental and economic reasons it is desirable to recycle sheet metal scrap, including that generated in the manufacture of automotive components from sheet aluminum. In the simplest sense, recycling of the scrap involves remelting the scrap to provide a body of molten metal that can be cast and rolled into useful aluminum sheet.
Frequently, however, automotive manufacturing scrap includes a mixture of scrap pieces of two or more aluminum alloys differing substantially from each other in composition. A specific example of mixed manufacturing scrap of aluminum sheet, generated in certain present-day automotive manufacturing operations, is a mixture of pieces of one or more alloys of the Aluminum Association 5000 series (with four-digit registration numbers between 5000 and 5999) and pieces of one or more alloys of the Aluminum Association 6000 series (with four-digit registration numbers between 6000 and 6999).
The presence of commingled pieces of different alloys in a body of scrap limits the ability of the scrap to be usefully recycled, unless the different alloys (or, at least, alloys belonging to different compositional families such as those respectively designated by the Aluminum Association series 1000, 2000, 3000, etc.) can be separated prior to remelting. This is because, when commingled scrap of plural different alloy compositions or composition families is remelted, the resultant molten mixture contains proportions of principal alloying elements (of the different compositions) that are too high to satisfy the compositional limitations of any particular commercial alloy. While it would therefore be beneficial to be able to sort a mass or body of aluminum sheet scrap containing a mixture of pieces of different alloys, to separate the different alloy compositions or at least different alloy families before remelting for recycling, scrap pieces of different aluminum alloy compositions are not ordinarily visually distinguishable from each other.
Published European Patent Application EP 0 861 910 A2 describes procedures for treating commingled aluminum scrap of two or more wrought aluminum alloys to impart different colors to surfaces of scrap pieces of different compositions for the purpose of sorting by alloy type or family (such as Aluminum Association series). The described procedures involve a separate step for introducing color onto the alloy before sorting, but after the alloy pieces of different compositions have become commingled, via a batch or semi-continuous chemical etch or series of etches. The chemical agents react with alloys of different compositions to produce discernable surface color differences between them. Methods for introducing color proposed include treatment with caustic, acid, oxidizing agents, dyes and combinations thereof.
That is to say, in the process of the European patent application, the marker is applied to every piece of scrap by a chemical treatment process and is subsequently detected by color differentiation. Treating every piece of scrap is inherently an expensive process, involving the performance of special, extra steps after the scrap is collected and before it can be sorted; and since the sortability of the commingled scrap is dependent on the ability of the treatment to react with different alloys to produce discernably different, composition-determined colors, there are limits to the coloring agents that can be used and/or to the types of alloys that can be differentiated.
An object of the present invention is to provide improvements in the sorting of metal scrap containing scrap pieces of different compositions, affording enhanced convenience and economy. Another particular object is to provide such improvements while avoiding a separate or special step of marking the scrap (i.e., after the scrap has been generated) to differentiate pieces of different compositions for such sorting. A specific object is to provide improved methods, affording the advantages just stated, of marking aluminum sheet to facilitate subsequent sorting of scrap including scrap pieces derived from the sheet together with scrap pieces of sheet of other aluminum alloys or alloy families.
To these and other ends, the invention embraces the application of surface marking to metal stock (i.e., metal produced or prepared in a form for working, cutting, etc., to manufacture articles or components), particularly aluminum sheet, prior to or during the performance of scrap-generating operations such as manufacturing operations.
In certain embodiments of the invention, the marking is performed by application of a marking agent to the stock or sheet during and as a part of procedures for preparing the sheet or other stock for subsequent scrap-generating manufacturing operations. For example, in preparing aluminum sheet for forming into automotive components or the like, it is conventional for the maker and supplier of the sheet to apply lubricant or prelubricant to surfaces of the sheet; in accordance with the present invention, the marking agent may be incorporated in the lubricant or prelubricant prior to application thereof to the sheet surfaces.
It is found that this method, utilizing a conventional sheet-preparing step for applying the marking agent and thereby avoiding any separate or added treatment of either sheet or scrap, can provide a detectable mark on surfaces of manufacturing scrap derived from the marked sheet, the marking agent being initially applied to the sheet in an amount effective to establish a deposit of mark-providing substance that will survive the scrap-generating manufacturing operations to which the sheet is subjected.
The term xe2x80x9cmarkxe2x80x9d as used herein is not limited to a deposit of marking agent which is visible or discernable as a mark on the original sheet; i.e., the marking agent provides a detectable mark on the scrap, not necessarily a visible mark on the sheet. Moreover, while in many instances detection of the mark may be performed by optical scanning, the detectable mark on scrap surfaces contemplated by the invention in its broadest aspects is not limited to a mark that is optically detectable, but also broadly includes a mark that is or can be detected in non-optical ways, e.g. by a sniffing device as used to detect drugs at airports, or by a laser that evaporates surface material in a puff or plume with a short pulse, with immediate analysis of the plume to identify the xe2x80x9cmarkxe2x80x9d substance.
The sheet to which the marking agent is applied may be of a single specific alloy composition, or may include sheet of two or more specific compositions within a compositional family (such as an Aluminum Association series, e.g., 1000, 2000, 3000, etc.) of which the members are sufficiently close in composition so that remelting of their commingled scrap provides a readily usable metal product. In the case where the manufacturing operations are such as to employ aluminum sheet of two composition families, generating scrap derived from sheet of both families, the marking agent is applied only to the sheet of one family, and not to the sheet of the other family, prior to the manufacturing operations. The residual optically detectable mark that thereby results, being present only on the surfaces of scrap pieces derived from sheet of the aforesaid one compositional family, enables easy sorting and separation of the pieces of the scrap into their respective compositional families, for remelting and recycling. Alternatively, different marking agents (respectively providing detectably different marks on scrap surfaces) may be applied to sheet of different alloy compositions or composition families, facilitating the sorting of scrap including scrap pieces of more than two compositions or families which are to be separated from each other.
Stated in some respects more broadly, the present invention concerns improvements in sorting metal scrap comprising a mixture of scrap metal pieces respectively derived from metal stock of at least two different compositions (e.g., at least two different compositional families), to separate the scrap metal pieces of a first of the compositions from the scrap metal pieces of a second of the compositions, the stock of each of the two compositions having a surface and being initially separate from the stock of the other of the two compositions, the scrap being generated and mixed during or after procedures performed on the stock of the two compositions, and the scrap metal pieces of each of the two compositions bearing visible portions of the surface of the stock from which they are derived. In this broad sense, the method of the invention embraces the steps of selectively applying a marking agent to the surface of only the stock of the first composition, prior to the performance of the aforesaid procedures, while the first-composition metal stock is separate from the metal stock of the second composition, the marking agent being applied in an amount effective to provide a detectable surface mark on surface portions on the scrap metal pieces of the first composition after the performance of the aforesaid procedures, such that the mark is present only on the scrap metal pieces of the first composition in the mixture, and scanning the mixture of metal scrap to detect the mark on scrap metal pieces therein, and thereby to distinguish the scrap metal pieces of the first composition from other scrap metal pieces in the mixture. Such a method typically further includes a step of segregating the scrap metal pieces on surface portions of which the mark is detected upon detection of said mark thereon in the scanning step.
The term xe2x80x9cscanningxe2x80x9d herein embraces ordinary visual scrutiny of the scrap with the human eye, in instances where the mark is discernable at visible wavelengths of light, with manual separation of scrap pieces, as well as scanning with apparatus e.g. of types currently commercially available and which may be capable of viewing the surfaces of the scrap pieces at ultraviolet, visible, or infrared wavelengths and mechanically sorting the scrap pieces in accordance with the presence or absence of a detected mark thereon. In addition, the term xe2x80x9cscanningxe2x80x9d is not limited to optical scanning but also includes non-optical scanning of the strip, e.g. by a sniffing device or a device that evaporates surface material and analyzes the resulting vapor plume to identify the mark substance, as mentioned above. In convenient embodiments, to which however the invention is not limited, the mark is a color, detectably present on visible surface portions on the first-composition scrap metal pieces, that is detectably different from the color of the unmarked second-composition scrap metal pieces.
The invention in this broad sense is applicable to the sorting of scrap of any metal, including (by way of example), steel, copper and magnesium alloys.
In an important particular aspect, the invention contemplates the provision of a method of applying a marking agent to aluminum sheet for scrap sorting purposes, comprising preparing aluminum alloy sheet of a first alloy composition for subjection to a manufacturing operation, the sheet having a surface, while applying to the sheet surface, incident to preparing the sheet as aforesaid, a marking agent in an amount effective to provide a detectable surface mark on scrap metal pieces derived from the sheet during or after the manufacturing operation and bearing visible portions of the sheet surface, thereby to enable scrap pieces of the sheet to be distinguished from scrap pieces of sheet of an aluminum alloy of other composition different from the first composition in a mixture of scrap metal pieces of the first and other compositions. Conveniently, the preparing step may be a surface treatment (e.g., a coating, washing, etching, prelubricating or lubricating step) which comprises applying a substance to the surface of the first-composition sheet, the method further including the step of incorporating the marking agent in the substance prior to application of the substance to the first-composition sheet surface. In specific embodiments, the applying step comprises incorporating the marking agent in a lubricant or prelubricant and applying the lubricant or prelubricant containing the marking agent to the sheet.
Where sheet of alloys of two different compositions (e.g. sheet of two different families of compositions) is being produced and prepared for manufacturing operations which will generate scrap comprising scrap metal pieces of both compositions, the method in particular embodiments includes preparing aluminum sheet of the first alloy composition for subjection to a manufacturing operation, and preparing aluminum sheet of a second alloy composition different from the first composition for subjection to a manufacturing operation, the second-composition sheet also having a surface, while selectively applying only to the surface of the first-composition sheet, and not to the surface of the second-composition sheet, incident to preparing the sheets as aforesaid, a marking agent in an amount effective to provide a detectable mark on scrap metal pieces derived from the first-composition sheet during or after the manufacturing operation and bearing portions of the first-composition sheet surface, thereby to enable scrap pieces of the first-composition sheet to be distinguished by scanning from scrap pieces of the second-composition sheet in a mixture of scrap metal pieces of the first and second compositions. Thus, where the applying step comprises incorporating the marking agent in a lubricant or prelubricant applied to the first-composition sheet, any lubricant or prelubricant applied in the step of preparing the second-composition sheet is essentially free of the marking agent.
In some instances, a different marking agent (providing a mark detectably different from that of the first-mentioned marking agent) may be applied to the second-composition sheet, for example by incorporating the second marking agent in a lubricant or prelubricant applied to the second-composition sheet surface prior to the manufacturing operations. This can be useful if the scrap contains more than two different compositions each of which is to be segregated from the others. In the case where the scrap is to be sorted into only two compositions (or composition families), however, it is convenient and economically beneficial to use only one marking agent, applied to sheet of only one of the compositions or composition families and providing a mark that, on the scrap pieces, enables the marked scrap pieces to be distinguished optically from unmarked scrap pieces. Thereby, the use of a second marking agent and the step of incorporating such a second agent in the lubricant for second-composition sheet are avoided.
In particular embodiments of current commercial interest, e.g. in the manufacture of automotive components, the first-composition sheet consists of sheets of one or more alloy compositions within a first family of alloys consisting of specifically different compositions having at least one shared compositional characteristic, and the second-composition sheet consists of sheets of one or more alloy compositions within a second family of alloys consisting of specifically different compositions having at least one shared compositional characteristic that differentiates the members of the second family from the first family. Illustratively, these families may respectively be the Aluminum Association 5000 and 6000 alloy series.
In another aspect, the invention embraces a method of sorting metal scrap generated incident to manufacturing operations performed on aluminum sheet of at least two different alloy compositions, the sheet of each composition having a surface and the scrap comprising a mixture of scrap metal pieces respectively derived from the aluminum sheet of each of the compositions and bearing visible portions of the surface of the sheet from which the pieces are derived, the method comprising subjecting, to the manufacturing operations, sheet of a first of the compositions bearing on its surface a marking agent applied thereto, prior to the manufacturing operations, in an amount effective to provide a detectable mark on the scrap metal pieces derived from the first-composition sheet, and sheet of a second of the compositions which is essentially free of the marking agent; and scanning the mixture of metal scrap to detect the mark on scrap metal pieces therein, thereby to distinguish the first-composition scrap metal pieces from other scrap metal pieces.
Embodiments of the invention such as those involving the addition of a fluorescent tracer-type marking agent to a lubricant or prelubricant conventionally supplied to the sheet by the sheet producer prior to delivery to a manufacturing customer, sometimes present a drawback in that the tracer-containing lubricant may be removed and/or transferred to scrap pieces of different composition (not initially bearing the tracer) incident to manufacturing procedures or subsequent handling and commingling of the scrap. When the marking agent is thus removed or transferred, the ability to distinguish between scrap of different compositions in the scanning step can be impaired or lost.
Accordingly, as a still further feature of the invention, in important preferred embodiments thereof, the step of selectively marking the stock surface of metal stock of only the first composition comprises applying a detectable marking to only those surface portions of the first-composition stock which will become surface portions of the scrap generated in the manufacturing procedure performed on the stock. Stated with reference to stamping operations for producing an article from stock and detaching scrap portions of the stock from the article, in these embodiments the marking is applied only to surface portions of the first-composition stock that will be detached as scrap and not to areas that will be included in the produced article.
This selective application of the marking only to areas of the stock that will be scrapped enables application of an indelible marking without compromising desired surface qualities or characteristics of the produced article. By xe2x80x9cindeliblexe2x80x9d is meant, in this sense, any mark that is not substantially removable from the stock or scrap surface, or transferrable to other surfaces (such as surfaces of scrap of different composition), in the manufacturing and subsequent scrap handling and commingling procedures to which the marked stock and scrap are subjected. A variety of paints and inks are suitably xe2x80x9cindeliblexe2x80x9d for application in such embodiments of the invention. More broadly, the indelible marking need not be an applied marking agent but can take the form of a detectable surface deformity such as an embossment applied, e.g. concurrently with a blanking operation or in some instances a stamping operation for producing an article, to areas of stock that are to be scrapped.
Thus, in such preferred embodiments the method of the invention contemplates selectively marking only surface portions, of stock of one composition, that will not be included in an article produced (by a stamping or other operation) from the stock, to establish on those selectively marked surface portions an indelible and detectable mark enabling scrap of the stock to be distinguished from unmarked scrap of other composition by a scanning step.
Further features and advantages of the invention will be apparent from the detailed description hereinafter set forth, together with the accompanying drawings.